The former Spain international has underlined the importance of the Atletico Madrid striker and is confident Vicente Del Bosque's men can defend the title.
The Atletico Madrid striker - who made his only appearance for Spain to date in March - has been troubled by a hamstring injury that curtailed his involvement in last weekend's Champions League final and is in danger of missing this summer's tournament.
Despite having earned just one cap, Hierro reckons that Costa could play a key role in Brazil and believes the Brazil-born forward is as important to Spain as Luis Suarez and Radamel Falcao are to Uruguay and Colombia respectively.PHOTOS: USA vs. Azerbaijan | World Cup teams
"The loss of a player like Suarez, Costa or Falcao would be a huge blow," he told AS. "They're very important for their national teams and I wish they were all there.
"It would be good for the competition. Strikers are artists whose goals decide matches."
Hierro then went on to urge Del Bosque to take a gamble on the 25-year-old forward if he is close to fitness and is confident Spain can become the first nation since Brazil in 1962 to win back-to-back tournaments.
"There were four players that weren't certain to go in 2010 and they were the stars who put the finishing touches before that winning goal," he referred to Jesus Navas, Fernando Torres, Cesc Fabregas and Andres Iniesta.
"I'm optimistic. I think a lot of this generation."